1. Field of the Invention
The present invention relates to a process for producing a polyarylene sulfide and an apparatus used in the process. More particularly, it pertains to a process capable of forming a uniformly dispersed state of a polymer phase in the case of separating a polymer phase from a solvent phase in producing a polyarylene sulfide, thus enabling production of a polyarylene sulfide having a high molecular weight; and an apparatus used in the process.
2. Description of the Related Arts
A polyarylene sulfide (hereinafter sometimes referred to as xe2x80x9cPASxe2x80x9d), especially polyphenylene sulfide is known as an engineering plastic which is excellent in mechanical strength, heat resistance and the like, and which has good electrical characteristics and high rigidity. Thus it is widely employed as various materials such as electronic parts and electrical parts. A number of proposals have recently been put forward on a process wherein polymerization is conducted by using a phase separation agent as a process of producing a polyarylene sulfide having a high molecular weight. The foregoing process sometimes involves such problems as causing a state that a polymer phase is separated form a solvent phase in a polymerization vessel after polymerization reaction, and in this case the polymer phase is settled by the difference in the specific gravity therebetween in a vessel bottom portion which is difficult to be influenced by shearing force due to agitation, thereby causing remarkable variance in the compositional ratio of the polymer phase to the solvent phase depending upon the position in the polymerization vessel.
As such in order to obtain a PAS having a high molecular weight, it is usually necessary to maintain the compositional ratio of the polymer phase to the solvent phase at a constant level in the polymerization vessel. As one of methods, it is taken into consideration to effect the polymerization while agitating the contents in the vessel under such conditions as uniformizing the above-mentioned compositional ratio. On the other hand, there is disclosed a polymerization method in which specially shaped agitational blades are used {Japanese Patent Application Laid-Open No. 290375/2000 (Heisei 12)}.
However, even with the aforesaid method, the uniformity of the polymer phase dispersion state is still insufficient and besides, in an attempt to obtain a PAS having a high molecular weight, sufficient agitational state is not assured as the case may be. In such circumstances, it has been eagerly desired to develop a process capable of producing a PAS having a high molecular weight.
It is taken into consideration as another method, to take out the polymer phase together with the solvent phase from the vicinity of the central portion in the depth direction of the vessel, said portion being considered to be in an average agitational state. In addition, there is disclosed a method in which a pool portion is provided at the bottom of the vessel, the polymer phase is withdrawn therefrom, and the solvent phase is withdrawn from a solvent pool installed at the top of the vessel so that the foregoing compositional ratio is kept constant {Japanese Patent Application Laid-Open No. 169844/1997 (Heisei 9)}. However, even with the foregoing method, the uniformity of the polymer phase dispersion state is still insufficient. Hence, it has been desired to develop a method capable of further uniformizing the dispersion state and besides, accurately controlling the compositional ratio of the polymer phase to the solvent phase. Further, it has been desired to develop a method capable of producing PAS with convenient and simple equipment without setting up a special pool portion as disclosed in the Patent Application mentioned above.
The present invention has been made in the light of the subject as mentioned above. A general object thereof is to provide a process capable of forming a uniform dispersion state of the polymer phase in a PAS polymerization vessel and thus producing a PAS having a high molecular weight, and to provide a PAS production apparatus usable in the aforesaid process.
Another object of the present invention is to provide a process capable of forming a uniform dispersion state of the polymer phase in a PAS polymerization vessel and also accurately controlling the compositional ratio of the polymer phase to the solvent phase, and also to provide a PAS production apparatus capable of forming a uniform dispersion state of the polymer phase therein with convenient and simple equipment, and also accurately controlling the compositional ratio of the polymer phase to the solvent phase.
Other objects of the present invention will become obvious from the text of this specification hereinafter disclosed.
In view of the foregoing objects, intensive extensive research and investigation were accumulated by the present inventors. As a result, it has been found that the objects of the present invention can be achieved by using a polymerization vessel equipped with baffles having specific arrangement and specific configuration. Further, it has been found that the objects of the present invention can be achieved by using a polymerization vessel equipped with agitational blades having specific configuration and specific arrangement. The present invention has been accomplished on the basis of the foregoing findings and information.
Specifically, the present invention provides a process for producing a polyarylene sulfide by the use of a polymerization vessel equipped with baffles, characterized by using the baffles that are asymmetrically arranged in a polymerization vessel, and/or in the form of round bar, and also provides an apparatus to be used in the above-mentioned process (hereinafter referred to as the first aspect of the present invention).
In addition, the present invention provides a process for producing a polyarylene sulfide by using a polymerization vessel equipped with an agitational blade, characterized by using the agitation blade which is devoid of a notch in the vicinity of the tip portion thereof, and which is in such a form as substantially equalizing the spacing between the tip portion thereof and the opposite bottom portion and/or end portion of a polymerization vessel all over the aforesaid tip portion, and also provides an apparatus for producing a PAS by using a polymerization vessel equipped with an agitational blade, characterized by using the agitation blade which is devoid of a notch in the vicinity thereof, and which is in such a form as substantially equalizing the spacing between the tip portion thereof and the opposite bottom portion and/or end portion of a polymerization vessel all over the aforesaid tip portion (hereinafter referred to as the second aspect of the present invention).
Furthermore, it has been found by the present inventors that the objects of the present invention can be achieved by separating a PAS resulting from polymerization into the polymer phase and the solvent phase, and immediately thereafter taking out at least part of the polymer phase settled in the lower portion of the polymerization vessel so that the polymer phase is prevented from agglomerating. That is to say, the present invention provides a process for producing a polyarylene sulfide by effecting polymerization in a polymerization vessel and then separating the same into the polymer phase and the solvent phase, characterized by withdrawing the polymer phase through a withdrawing portion provided on the end plate of the aforesaid polymerization vessel, and also provides an apparatus for producing a polyarylene sulfide by the use of a polymerization vessel equipped with an agitational blade, characterized in that said apparatus is equipped with a withdrawing portion which is placed on the end plate of the above-mentioned polymerization vessel, and is protruded into the vessel by a protrusive length of 0 to 80% of the spacing between the tip portion of the agitational blade and the opposite bottom portion (hereinafter referred to as the third aspect of the present invention).